Recently, plasma display panels (hereafter referred to as PDPs) have become the focus of attention for their ability to realize a large, slim and lightweight display apparatus for use in computers, televisions and the like.
PDPs can be broadly divided into two types: direct current (DC) and alternating current (AC). Of these, AC PDPs are at present the dominant type.
In a typical AC PDP, a front substrate and a back substrate are placed in parallel so as to face each other. A scanning electrode group and a sustain electrode group are formed in parallel strips on the inward-facing surface of the front substrate. The electrode groups are covered by a dielectric layer. A data electrode group is formed in parallel strips perpendicular to the scanning electrode group, on the inward-facing surface of the back substrate. The space between the front substrate and the back substrate is divided into smaller spaces by the stripe ribs. Discharge gas is sealed in these spaces. Discharge cells are formed in the space between the substrates, at the points where the scanning electrodes and the data electrodes intersect, the discharge cells as a whole thus forming a matrix.
When a PDP is activated, each discharge cell is turned on or off through a sequence of the periods: an initialization period in which all discharge cells are initialized by applying an initialization pulse; a write period in which pixel information is written by applying a data pulse to data electrodes selected from the data electrode group while sequentially applying a scanning pulse to the scanning electrodes; a discharge sustain period in which light is emitted by sustaining a main discharge by applying a rectangular-wave sustain pulse to a space between the scanning electrode group and the sustain electrode group; and an erase period in which wall charge of the discharge cells is erased.
Each discharge cell is fundamentally only capable of two display states, ON and OFF. Here, an in-field time division gray scale display method in which one frame (one field) is divided into a plurality of sub-fields and the ON and OFF states in each sub-field are combined to express a gray scale is used.
In such a PDP, it is a significant challenge to drive the PDP with a small amount of power consumption. To reduce the power consumption for driving PDP, it is desired to improve the luminous efficiency by reducing the amount of power consumption in the sustain period. The problem of the power consumption becomes more significant when wide transparent electrodes are used to improve the luminance in image display. This is because the wide transparent electrodes consume a lot of power.
To suppress the discharge current from increasing, some attempts have been made. One of such attempts is to reduce the area of electrode per discharge cell by making an opening in each transparent electrode or by dividing each electrode into a plurality of line electrodes. However, in this type of electrode, a voltage drop is apt to be caused at the electrode terminal, or when a drive pulse is applied, the discharge current is apt to separate into a plurality of peaks. When this happens, the light-emission luminance tends to greatly depend on the drive voltage.
When the gray scale is represented by the length of the sustain period (that is, by the number of sustain pulses), the discharge current in the whole panel varies as the number of turned-on discharge cells on the panel greatly changes depending on the image signal. However, when the light-emission luminance depends on the drive voltage greatly as described above, the effective drive voltage applied to the discharge cells varies. Accordingly, in such a case, it is difficult to control the gray scale. This is another problem.
On the other hand, the PDP, as well as other types of displays, is becoming to have higher definition. With this tendency, the length (that is, time period) of the write pulse is becoming shorter. For example, for displaying full-color moving pictures, the write pulse width in the write period is defined as no longer than 2.5 μs, and for the full-spec high-definition (highly minute with the number of scanning lines being 1080) the write pulse width is defined as 1–1.3 μs, which is very short.
Too short a time period of the write pulse causes a write defect, degrading the image quality. As a result, it is desired that to achieve a high-definition PDP, the DPD is driven at a high speed by reducing the write pulse to be shorter than the sustain pulse width, and allowing the PDP to emit light with high luminance.
When a simple rectangular wave is used as the sustain pulse, if the data pulse width is set to approximately 2 μs or shorter, the discharge probability at the sustain discharge decreases, and this is apt to cause the image quality degradation.
In such conditions, a technique for driving the sustain pulse at a high speed is also desired.